The present invention relates to the production of carbon dioxide from a subterranean formation and more particularly relates to a method of completing a carbon dioxide well to alleviate the corrosive effects of produced carbon dioxide on the casing and tubing strings in the well.
It has long been recognized that carbon dioxide may be injected into an oil-bearing formation during a secondary or tertiary enhanced recovery operation to produce additional amounts of oil. One of the most attractive sources for carbon dioxide for this purpose is natural subterranean formations which produce large volumes of almost pure carbon dioxide. Unfortunately, many of the known formations capable of producing carbon dioxide in quantities sufficient for enhanced oil recovery operations are located several hundred miles from the oil fields in which the carbon dioxide is to be used. Accordingly, the carbon dioxide must be gathered from the carbon dioxide producing wells, treated, and then pipelined to several hundred miles to its final destination. Due to the physical properties of carbon dioxide, it normally arrives at the surface from a production well in a two-phase state. As is known, flowing such a two-phase fluid through a pipeline over long distances of varying elevations creates a fluid "hammer" effect which is likely to cause serious damage to the pipeline and related equipment as well as considerable loss of horsepower. Therefore, the carbon dioxide has to be gathered and processed at or near the production wells and delivered to the pipeline as a single phase fluid, either gas, liquid, or supercritical fluid.
One method for producing and gathering carbon dioxide in a single supercritical phase is fully disclosed in copending U.S. patent application Ser. No. 38,034, filed May 10, 1979. This method involves lowering a pump means into a carbon dioxide production well to boost the pressure of the carbon dioxide downhole to value sufficient to insure that the carbon dioxide produced at the surface will have a pressure greater than its critical pressure.
However, in the above-mentioned production method, it has been found that when carbon dioxide rises in the annulus formed between the well casing and the tubing string, it expands due to the reduction in temperature and pressure and water vapor carried by the carbon dioxide condenses onto both the interior surface of the casing string and the exterior surface of the tubing string. This water in conjunction with carbon dioxide in the annulus forms carbonic acid which when in contact with the steel casing and tubing causes extreme corrosive conditions which normally leads to rapid deterioration and failure of the casing and/or tubing strings.